Concrete construction methods conventionally utilized forms for the placement, finishing and curing of concrete. The application of those forms to foundation structures, such as slabs, mats, footings and to pavements, usually required considerable preparation of the subgrade for providing a support surface for static and/or dynamic loading conditions. That frequently necessitated the compaction of the underlying soil and/or fill material, placement of successive layers of sand, crushed stone and gravel for distributing the superimposed loads and for drainage purposes. Also, the prepared base had to be moistened to reduce the absorption of water from the freshly poured concrete. Alternate steps included providing a vapor barrier which was usually in the form of a polyethylene sheet placed directly on the prepared base and the installation of side forms or "headers" to define the perimeter of the structure. That construction procedure further required the setting of reinforcing steel, usually in the form of wire mesh or wire fabric, to preserve aggregate interlock and prevent surface cracks. That reinforcement was placed upon chairs which were designed to support the reinforcement at a desired location below the finished grade of the concrete. The concrete, in a plastic state, was then deposited within that form arrangement and, after curing, the form had to be stripped.
A problem with seating wire fabric, as described above, was that when the concrete was poured, the wire mesh tended to drape and, therefore, it was difficult to keep the reinforcement at a constant design depth below the finished grade.
A further shortcoming of those construction methods was that the forms did not provide an optimum distribution of concrete but, rather, relied upon a uniform maximum thickness throughout even though not structurally required for withstanding compressive stresses under actual load conditions. Other attempts to modify concrete sections, so as to reduce the volume of concrete, appeared in structural members incorporated into floor systems, such as metal-pan, cellular and corrugated steel forms.
Reference is also made to the above ground floor slabs illustrated in U.S. Pat. No. 3,334,458. The relief form of this invention in contrast is adapted primarily to accommodate the concrete on grade and conforming to the configuration of the form rather than to function as an integral structural member.
Another disadvantage was that the multistep procedure of the prior art was not cost effective with regard to materials, time and labor.